1. Field of the Invention
The present invention relates to a navigation system for vehicle in which a current position of a vehicle is detected, map data of a specific area including the current position is read out from a recording medium, and a route from the current position to a received destination is determined according to the map data to guide the vehicle to take the route to the destination along the route by using picture and voice.
2. Description of Related Art
In a conventional navigation device for vehicle, a current position of a vehicle is detected by using a global positioning system (GPS), road map data and information relating to a road map are read out from a recording medium (for example, a compact disk) mounted on a disk unit, a route from the current position to a destination input by a user is determined according to a Dijkstra method, and the vehicle is guided to take the determined route to the destination by using picture and voice.
In this case, the road map data and the information relating to a road map are in advance read out from the recording medium to a memory of a data buffer. Therefore, the user can gain access to the road map data and the information stored in the data buffer memory at high speed.
The road map data and the information are successively read out while performing the navigation operation during the movement of the vehicle. Therefore, the road map data and the information can be read out without delay. However, the user sometimes requires that the navigation device for vehicle has a function other than the navigation function. In this case, it is required that the disk unit of the navigation device can be used to read out not only the road map data recording in a map recording medium but also another type of data recorded in another recording medium. Therefore, in recent years, as is described in Published Unexamined Japanese Patent Application No. H9-96532 of 1997, a pre-reading process is performed prior to the performance of the navigation to set the disk unit to a standby condition after the pre-reading process. Therefore, even though the navigation function is performed by the conventional navigation device for vehicle after the pre-reading process, a function other than the navigation function can be performed by using the disk unit during the navigation.
FIG. 6 schematically shows a plurality of map units of a map area to explain a pre-reading process in which map data of map units placed around a route is in advance read out prior to the navigation in the conventional navigation device for vehicle.
As shown in FIG. 6, a map area indicated by map data is partitioned into a plurality of map units. Each map unit has a squared area which is 1 km by 1 km. Also, each of all roads (not shown) of the map area indicated by the map data is divided into a plurality of links, and a route from a current position to a destination is placed on a road or a plurality of roads. Therefore, the route is composed of a plurality of links (hereinafter, called route links) corresponding to a plurality of parts of the route.
Each map unit including at least one route link is indicated by a densely hatched squared area and is called a route link map unit. Each map unit adjacent to one route link map unit is indicated by a sparsely hatched squared area and is called an adjacent map unit. Also, the other map units are respectively indicated by a non-hatched squared area. A pre-reading process is performed for the route link map units and the adjacent map units. That is, when a route from a current position to a destination is determined by a route determining unit according to map data, map data corresponding to both route link map units and adjacent map units is read out as map data relating to the route from a recording medium and is stored in a memory of a data buffer. Therefore, the user can gain access to the map data relating to the route stored in the memory of the data buffer at high speed. In contrast, no data of map units other than the route link map units and the adjacent map units is stored in the memory of the data buffer.
The route links of the route are identified by a plurality of identification names (that is, L1, L2, L3, - - - ) expressed by consecutive numbers. Because map data indicates two-dimensional area, each map unit is identified by an identification number M(i,j). Each route link is included in one route link map unit, and no route link is included in a plurality of map units. Therefore, only one route link map unit M(i,j) including an arbitrary route link Lk exists. Also, one route link map unit can include a plurality of route links. Therefore, one route link map unit can include all the route.
For example, three route links L1, L2 and L3 are included in the route link map unit placed on the most left side of the route.
FIG. 7 is a flow chart showing the procedure of the pre-reading process performed for the map data prior to the navigation performed in the conventional navigation device for vehicle. The procedure of the pre-reading process will be described below with reference to FIG. 6 and FIG. 7.
In a step ST11, to initially perform the pre-reading process for the route link L0, k=0 is set. In a step ST12, map data of a route link map unit M(i,j) including a route link Lk and map data of eight adjacent link map units M(ixe2x88x921,jxe2x88x921), M(i,jxe2x88x921), M(ixe2x88x921,j), M(ixe2x88x921,j+1), M(i+1,j), M(i,j+1), M(i+1,jxe2x88x921) and M(i+1,j+1) adjacent to the route link map unit M(i,j) are read out from a recording medium and are stored in a memory of a data buffer.
In a step ST13, it is checked whether or not the route link Lk is a final part of the route. In other words, it is checked whether or not the pre-reading process for the route from the current position to the destination is completed. In cases where the route link Lk is a final part of the route, the procedure proceeds to a step ST14, and the pre-reading process is completed.
In contrast, in cases where the route link Lk is not a final part of the route, the number k is incremented. That is, k=k+1 is set. Thereafter, the steps ST12 and ST13 are again performed.
As is described above, to make preparations for the use of a function other than the navigation function in the conventional navigation device for vehicle, it is required that the disk unit is set to a standby condition. Therefore, the disk unit is in advance used for the pre-reading process to transfer map data of the route link map units and map data of the adjacent map units from a recording medium to a memory of a data buffer, and the user can gain access to the map data of the route link map units and the map data of the adjacent map units stored in the memory of the data buffer at high speed.
However, in cases where a length of a route from a current position of a vehicle to a destination is extremely long, because a storage capacity of the data buffer is limited, it is impossible to write road map data of all route link map units and all adjacent map units relating to the extremely long route in the data buffer. Therefore, only a part of the road map data is written in the data buffer, but the other parts of the road map data cannot be written in the data buffer. In this case, each time the part of the road map data written in the data buffer is used for the navigation function, it is required that another part of the road map data is written in the data buffer. In this case, to write another part of the road map data in the data buffer, it is required that a recording medium of the road map data is again mounted on the disk unit. Also, it is sometimes required that another recording medium used for a function other than the navigation function is demounted from the disk unit to mount the recording medium of the road map data on the disk unit.
Also, because it is required that the recording medium of road map data and the recording medium used for a function other than the navigation function are alternately selected and mounted on the disk unit, it is troublesome for a driver when the driver drives the vehicle. Also, when the changeover of one recording medium to another one is performed, the performance of a function other than the navigation function is interrupted. Therefore, a problem has arisen that the user cannot sufficiently use a function other than the navigation function.
A main object of the present invention is to provide, with due consideration to the drawbacks of the conventional navigation device for vehicle, a navigation device for vehicle in which an additional function performable by using a map data providing unit is sufficiently performed in addition to a navigation function.
Also, a subordinate object of the present invention is to provide a navigation device for vehicle in which a user easily uses an additional function performable by using a map data providing unit without troublesomeness.
The main object and the subordinate object are achieved by the provision of a navigation device for vehicle comprising map data providing means for reading map data from a recording medium, pre-reading process means for receiving a destination, detecting a current position of a vehicle, determining a route from the current position of the vehicle to the destination according to the map data provided from the map data providing means, setting an area of a first map corresponding to a first part of the route placed in a first type of road to a first range in a pre-reading process and setting an area of a map corresponding to a second part of the route placed in a second type of road to a second range in the pre-reading process on condition that the second range of the area of the second map is narrower than the first range of the area of the second map, data storing means for storing both first map data, which corresponds to the first map area set by the pre-reading process means and is provided from the map data providing means, and second map data, which corresponds to the second map area set by the pre-reading process means and is provided from the map data providing means, in the pre-reading process, and guiding means for guiding the vehicle to take the route to the destination according to both the first map and the second map which are indicated by both the first map data and the second map data stored in the data storing means.
Therefore, a data volume of the map data stored in the data storing means can be considerably reduced.
Accordingly, even though the length of the route is long, the map data relating to the route can be stored in advance in the data storing means according to the pre-reading process. Also, because a time required to store the map data relating to the route in the data storing means can be shortened, an additional function other than the navigation function can be sufficiently performed by using the map data providing means. Also, the requirement of the additional storage of the map data relating to the route in the data storing means is reduced. Therefore, the number of mounting operations of the map recording medium on the map data providing means can be reduced. Accordingly, a user can easily use an additional function other than the navigation function by using the map data providing means without troublesomeness.
It is preferred that the pre-reading process means comprises road attribute checking means for receiving the map data of a map area, which is partitioned into a plurality of map units and includes both the first type of road, to which a road attribute indicating the first type of road is attached, and the second type of road to which a road attribute indicating the second type of road is attached, from the map data providing means, partitioning the route placed on both the first type of road and the second type of road into a plurality of route links respectively included in one of the map units so as to attach the road attribute indicating the first type of road or the road attribute indicating the second type of road to each route link, checking whether the road attribute attached to each route link indicates the first type of road or the second type of road, specifying a first remarked map unit including each first remarked route link and one or a plurality of map units placed near to the first remarked map unit in cases where the road attribute attached to the first remarked route link indicates the first type of road, specifying a second remarked map unit including each second remarked route link in cases where the road attribute attached to the second remarked route link indicates the second type of road, controlling the data storing means to store data of the first remarked map units and data of the map units placed near to the first remarked map units as the first map data and controlling the data storing means to store data of the second remarked map units and data of the map units placed near to the second remarked map units as the second map data.
Therefore, a data volume of the map data stored in the data storing means can be reliably reduced. Accordingly, even though the length of the route is long, the map data relating to the route can be stored in advance in the data storing means according to the pre-reading process. Also, a time required to store the map data relating to the route in the data storing means can be shortened, and an additional function other than the navigation function can be sufficiently performed by using the map data providing means. Also, the requirement of the additional storage of the map data relating to the route in the data storing means is reduced, and the number of mounting operations of the map recording medium on the map data providing means can be reduced. Accordingly, a user can easily use an additional function other than the navigation function by using the map data providing means without troublesomeness.
It is preferred that the first type of road denotes a general road other than a throughway, and the second type of road denotes a throughway.
Because a user does not desire a map corresponding to an area adjacent to the throughway, data volume of the map data stored in the data storing means can be reasonably reduced.
It is preferred that one or a plurality of map units placed near to one second remarked map unit are specified by the road attribute checking means in cases where a junction exists in the second remarked map unit, and the data storing means is controlled by the road attribute checking means to additionally store data of the map units placed near to the second remarked map unit as the second map data.
Because there is high probability that the user changes his destination when the vehicle running on a throughway approaches a junction, map data of an area near to the junction is additionally stored in data storing means in the pre-reading process. Therefore, the navigation function can be performed according to the map of the area around the junction. Accordingly, the user can reliably recognize the existence of the junction on the map.
Also, because the user can reliably recognize the existence of the junction on the map, the user can keep on the route without taking a wrong road at the junction. Also, even though the user takes a wrong road differing from a correct route at the junction, because the navigation function is performed according to the map of the area around the junction, a probability of the returning of the user to the correct route can be heightened without again mounting a map recording medium on the map data providing means.
It is preferred that a second pre-reading process is performed by the road attribute checking means to specify one or a plurality of additional map units placed near to the map units which are placed near to the first remarked map unit or the second remarked map unit, and the data storing means is controlled by the road attribute checking means to additionally store data of the additional map units.
In cases where there is a free space in the data storing means after the completion of the pre-reading process, the second pre-reading process is performed.
Accordingly, even though the user takes a wrong road differing from a correct route, a probability of the returning of the user to the correct route can be heightened without again mounting the map recording medium on the map data providing means. Also, even though a function other than the navigation function is not used in the navigation device for vehicle, resources of the map data providing means and the data storing means can be effectively used.
It is preferred that the map data providing means is formed of a communication unit, connected with an internet, for downloading the map data from an external server and providing the map data for the pre-reading process means and the data storing means.
Therefore, updated map data can be always used in the navigation device for vehicle without increasing the storage capacity of the data storing means.